Significance: Over 67% of American adults are obese or overweight. This health epidemic is costly and associated with multiple chronic illnesses including, type 2 diabetes, cancer, and cardiovascular diseases. Many people who lose weight gain it back; this is attributable to individuals' failure to self-regulate and maintain regular physical activity, follow a low-fat diet, and monitor body weight. While many intervention strategies succeed at initiation of weight-control behaviors, they often fail to facilitate behavior maintenance and prevent relapse of weight gain. Limited empirical evidence exists on how to sustain weight-loss and weight-control behaviors, and thus prevent relapse. The rate of weight gain is highest immediately after cessation of a structured weight-loss program. Needed are intervention strategies that can be used following a structured weight-loss program that promote sustainability of weight-loss, that prevent relapse, and that are easy and affordable to use. Methods: A three-month randomized controlled design study will be used to evaluate the effect of tailored short message service (SMS), also known as text messaging, on weight-loss sustainability and relapse. 60 obese (BMI>30) people (30 males), who have lost at least 5% of their body weight, will be recruited from the Duke University Diet and Fitness Center (DFC) following a four week diet and exercise program where people lose an average of 5% of initial weight. Participants will be randomized into an experimental or control group. The experimental group (n=30) will receive SMS that match their regulatory focus orientation (prevention or promotion focus). The control group (n=30) will receive SMS that do not match their regulatory focus orientation. Both groups will receive SMS daily for one month. Message content will be constructed by the researcher, an expert consultant, and a team of nutritionists, exercise physiologists, and physicians at the DFC. Participants will complete surveys at baseline and 3 months post-baseline assessing BMI. Four focus groups will be conducted from a sample of the participants to assess perceived usefulness, attitudes, and experiences of participating in the study. PUBLIC HEALTH RELEVANCE: Over 67% of American adults are obese or overweight. This health epidemic is costly and linked to many chronic illnesses. This includes type 2 diabetes, cancer, and heart disease. Many people who do lose weight gain the weight back. Thus, interventions are needed that help sustain weight loss. By sustaining weight loss, relapse of weight gain can be prevented and the prevalence of obesity reduced.